Certain severely handicapped people can only reliably communicate through their eye movements. To facilitate this communication, typewriting devices have been developed which utilize eye-position control. An example of such a system is described in an article entitled "Eye-Controlled Communication Aids" by J. H. ten Kate et al., Medical Progress Through Technology 8:1-21, Springer-Verlag 1980. Eye tracking or positioning devices have also been described in U.S. Pat. No. 3,507,988 entitled "Narrow-Band, Single-Observer, Television Apparatus" by William S. Holmes, issued Apr. 21, 1970; U.S. Pat. No. 3,724,932 entitled "Eye Tracker And Method" by Tom N. Cornsweet et al issued Apr. 3, 1973. Reference to eye tracking devices is also made in U.S. Pat. No. 4,513,317 entitled "Retinally Stabilized Differential Resolution Television Display" by Carl F. Ruoff, issued Apr. 23, 1985. In general, these devices use a photo-sensor which detects the change in diffused or specular infrared reflections from the eye as it moves. A limiting factor in the detection of eye movements for communication purposes is the non-linearity of the transducer. As a result, eye tracking calibration has often been difficult, time consuming and inconsistent.